Patent EA-003855-B1 (EA)
Title: Measurement of magnetic fields using a string fixed at both ends
Inventor: VERYASKIN ALEXEY VLADIMIROVICH
IPC: G01R33/022
Filed: 2000-05-11
Abstract: 1. Apparatus for magnetic gradiometry comprising: a string (1) fixed at both ends, held under tension and arranged to carry a current; and at least two sensors (L1, L2) symmetrically longitudinally positioned about the mid-point of said string and arranged to detect the transverse displacement of said string from an unperturbed position, due to a magnetic field acting on said string. 2. Apparatus as claimed in claim 1, wherein it contains an alternating current generator for skipping of the alternating current through the string (1). 3. Apparatus as claimed in claim 2, wherein the generator provides forming of the alternating current with frequency, which is substantially equal to the frequency of a natural anti-symmetric mode of said string (1). 4. Apparatus as claimed in claim 3, wherein the generator provides forming of the alternating current with frequency, which is twice the fundamental frequency of the string (1). 5. Apparatus as claimed in any of claims 2 to 4, wherein the sensors are arranged to generate a detection signal due to the transverse displacement of the string and the apparatus further comprises demodulating means (9) arranged to demodulate the detection signal with a demodulation signal, the demodulation signal having a frequency twice that of the alternating current. 6. Apparatus as claimed in any preceding claim, wherein said sensors comprise at least one pick-up coil (L1, L2) arranged such that, in use, a current is induced in the coil by the current passing through the string (1). 7. Apparatus as claimed in any preceding claim comprising means for detecting the transverse displacement of said string (1) in two non-parallel planes. 8. A method of magnetic gradiometry comprising: providing a string (1) fixed at both ends, held under tension and carrying a current; and detecting, by means of at least two sensors (L1, L2) symmetrically longitudinally positioned about the midpoint of said string, the transverse displacement of said string from an unperturbed position, due to a magnetic field acting on said string. 9. A method as claimed in claim 8, wherein the alternating current is skipping through the string (1). 10. A method as claimed in claim 9, wherein the frequency of the alternating current is substantially equal to the frequency of a natural anti-symmetric mode of said string (1). 11. A method as claimed in claim 10, wherein the frequency of the alternating current is twice the fundamental frequency of the string (1). 12. A method as claimed in any of claims 9 to 11, wherein the step of detecting the transverse displacement of the string (1) includes demodulating a signal due to the displacement of the string with a demodulating frequency, which is twice the frequency of the alternating current through the string. 13. A method as claimed in any of claims 8 to 12, wherein the displacement of the string (1) is detected by electromagnetic means. 14. A method as claimed in any of claims 8 to 13, wherein the displacement of the string (1) is detected in two non-parallel planes.